Inflammatory demyelinating polyradiculoneuropathy, especially its acute form (Guillain-Barré syndrome) is a frequent cause of flaccid paresis. It is an immunological disease and its aetiology is often unknown. In severe forms good therapeutic effects are obtained with plasmapheresis or intravenous administration of human immunoglobulins. Very important is monitoring of respiratory efficacy and circulatory functions, as well as symptomatic treatment. Immunosuppresion is applied in justified cases.